Bring a large pot of salted water to a boil.
Meanwhile, heat 2 tablespoons olive oil in a
large skillet over medium heat. Add the sausage
and cook, breaking up the meat with a wooden
spoon, until browned, about 3 minutes. Add the
scallion whites and rosemary and cook until the
scallions begin to wilt, about 2 minutes. Add
the tomatoes with their juices and 1/2 cup of
the boiling water. Let simmer while you cook
Add the pasta to the pot of boiling water and
cook as the label directs for al dente. Reserve
1/2 cup cooking water, then drain.
Add the pasta to the tomato sauce along with
the spinach and half of the scallion greens.
Toss to coat the pasta and wilt the spinach,
about 1 minute, gradually adding the reserved
pasta water as needed to loosen. Season with
salt, drizzle with the remaining 1 tablespoon
olive oil and remove from the heat.
Sprinkle the cheese over the pasta and toss
well. Divide among plates or shallow bowls and
top with the remaining scallion greens.